1. Field of the Invention
The invention relates generally to recording scrambled television signals and, more specifically, relates to apparatus for recording scrambled television signals automatically without requiring a timer for subsequent playback in an unscrambled mode.
2. Description of the Prior Art
Television broadcasting systems are now well known in which a broadcasting station transmits a scrambled or coded television signal and the consumer, after making the appropriate technical and financial arrangements with the broadcasting company, receives the signal and descrambles or decodes it by means of a decoder supplied by the broadcasting company for viewing.
One example of this kind of scrambled signal television broadcasting system transmits a video signal that is periodically inverted in polarity for a predetermined period of time or that is periodically changed in order or sequence for a predetermined period of time. A corresponding code to correct the polarity or sequence of the signals is provided in a decoder at the receiver, whereby the transmitted signals are decoded prior to viewing.
There also has been proposed a system in which a transmitting scrambled television signal is received and recorded directly in scrambled form by a video tape recorder (VTR) and, subsequently, the recorded, scrambled signal is played back through a decoder for viewing. In such proposed system, the scrambled signals are broadcast during times other than usual broadcast hours for prime time programming, for example, after midnight, and the signal is then recorded automatically using a timer. Thus, the exact time that the scrambled program is to be broadcast and the exact length of such program must be known ahead of time and, if not, the automatic recording of the scrambled broadcast cannot be accomplished satisfactorily. Another problem is that the automatic timers on many VTR's are difficult for the average consumer to set properly and, frequently, the desired program is not recorded correctly. Furthermore, in the case of brief power outages not only will the clock in the video tape recorder be slow, thereby causing the first portion of the desired program to be missed, but also the setting in the timer of most VTR's is cleared when losing power and, thus, no recording will take place.